Timber Products Types • Natural Timbers • Engineered Timbers Natural Timbers • Structural • Non Structural Structural Timbers • BCA Requirements Performance Requirements – Volume 1 Structural Timbers • BCA Requirements Performance Requirements – Volume 1 AS 1684 & Volume 1 AS 1684 & Volume 1 Structural Timbers • BCA Requirements Performance Requirements – Volume 2 AS 1684 & Volume 1 Natural Timber • Different Timbers have different Characteristics • Different Strengths • F5, F7, F8, F11, F14, F17, F22 & F27 • MGP 10, MGP 12 & MGP 15 Grades of Structural Timbers • AS 1684.2 Timber Grading Methods • Visual • Machine Stress Grading Stress Grading - Visual • Traditional Method • Still used in Australia for – Hardwoods – Softwood – Large Sections • Trained Grader Stress Grading - Visual • Every piece of timber produced is visually inspected • Hardwood or Softwood visual grading standards define rules, as to the types sizes and positions of 20 physical characteristics that are allowed into each 'group' or structural grade of material. • The size and position of knots and other potential strength reducing characteristics in each piece is compared with the size and position of these characteristics allowed in the various grading classifications. • The highest grades allow fewer and smaller characteristics in each piece of timber. Stress Grading - Visual • Visual Graded Timber are “F” grade – E.g. F5, F8 F14 etc. • Structural grading has no correlation with aesthetic appearance Structural Defects Strength Limiting Characteristics -Pith • In softwoods, pith is the dark spot that was the upward growing twig when the tree was very young. It signifies the presence of 'core wood' or 'juvenile wood'. Where the density of the wood is low, this can reduce the strength of the timber. In grading of softwoods, the visual grader has to estimate the spacing of the annual rings to determine whether or not a piece with core wood is within the specification of this grade. Strength Limiting Characteristics -Pith Strength Limiting Characteristics – Surface Checks • Surface checks are shallow cracks on the surface, mainly from the release of residual stresses on drying. The grader must check all cracks to see that they are not a split (that runs from one face to the other), and if a check (shallow crack) that they are not too wide, or too long. Strength Limiting Characteristics – Surface Checks Checking Splitting • A longitudinal separation of the fibres which extends to the opposite face of a piece of sawn timber. Strength Limiting Characteristics – Knots • Depending on the location of the knots, different limits apply. They are estimated by the Knot Area Ratio (KAR) which requires a grader to visualise the knots going right through the cross-section. The KAR is the percentage of the cross-section that is taken up with knots. Different limits on KAR apply for knots in the margin (outer quarter of the wide face) and for the centre (central half of the wide face). Strength Limiting Characteristics – Knots Strength Limiting Characteristics – Resin or Bark Pockets • Resin or bark pockets are gaps in the wood where the growing tree has captured some bark or resin. The bark or resin may still be there, but often it has disappeared leaving an empty dark-coloured pocket. All resin or bark pockets must have their width and length estimated. A piece is classed as within the grade where the pocket is smaller than the published size limit. Strength Limiting Characteristics – Resin or Bark Pockets Strength Limiting Characteristics – Wane • Wane is usually seen as a missing corner, as the outside of the tree falls within the cross section. If more than the limiting percentage is missing, then the piece falls below the grade specification. Wane is caused by mechanical damage to the timber during processing Strength Limiting Characteristics – Wane Strength Limiting Characteristics – Spring & Bow Spring and bow are deformations in the unloaded timber. The grader must be able to estimate how far from being straight the piece is over the designated lengths. Bow • A curve along the face of a board that usually runs from end to end. Spring • Warping along the edge from one end to the other. This is most common in wood that was cut from the centre of the tree near the pith. Assigning Grades • Each species of timber listed in the visual grading standard has been tested (as small clear specimens) to find the strength of the wood fibre. This is used to assign a strength group to each species. Wood with stronger fibres has a higher strength group indicating its potential to deliver stronger pieces if there are not too many strength limiting characteristics. Timber Grading Methods • Visual • Machine Stress Grading Machine Stress Grading Machine stress-grading uses a machine to bend each piece of timber (generally about its minor axis). The machine measures the stiffness of the piece and uses a loose correlation between stiffness and strength to assign a stress grade. Machine Stress Grading Machine Stress Grading Machine Stress Grading Machine Stress Grading • Radiata Pine is the only timber that is Machine Graded • Machine Stress Graded Timber is designated MGP Tolerances - Structural • AS 1684 – The Law in regards to Structural Requirement Durability of Timber • Fungal Attack • Termite Attack • Thermal Attack • Chemical/Liquid Attack Fungal Degradation • Fungi can be broadly grouped into two main types, 1. Moulds and stains (i.e. blue stain) usually only mar appearance (blue stain can effect impact strength) 2. Rot fungi (white rot, brown rot and soft rot) can significantly effect strength properties as they penetrate or break down the cell walls of wood. – DRY ROT Dry Rot • Fungal Decay caused by Serpula lacrymans • The decayed wood takes on a dark or browner crumbly appearance, with cubical like cracking or checking, that becomes brittle and can eventually crush the wood into powder. • Eventually the decay can cause instability and collapse in structures. Dry Rot Fungal Degradation – Dry Rot • Timber is only vulnerable to fungal attack if the four following conditions are met: – Moisture – Oxygen – Temperature – Nutrients Moisture • Moisture must be present; if the timber moisture content (MC) is between 0 and 20%, fungal attack will not occur. Between 20-25% MC fungal attack is retarded, and fungal attack occurs when the MC is over 25%. Fungal Degradation • Timber is only vulnerable to fungal attack if the four following conditions are met: – Moisture – Oxygen – Temperature – Nutrients Oxygen • Oxygen must be present; timber that is completely submerged, saturated, or more than 600 mm below ground is rarely attacked. Fungal Degradation – Dry Rot • Timber is only vulnerable to fungal attack if the four following conditions are met: – Moisture – Oxygen – Temperature – Nutrients Temperature • Temperature must be in the range of 5° to 40°C; 25° to 40°C is ideal. • Fungal attack is retarded by higher or lower temperatures. Fungal Degradation – Dry Rot • Timber is only vulnerable to fungal attack if the four following conditions are met: – Moisture – Oxygen – Temperature – Nutrients Nutrients • Food must be present in the form of unprotected nutrients (carbohydrates, nitrogen minerals, etc.). The timber usually provides these itself, particularly sapwood, which is normally high in sugars and carbohydrates. Nutrients in the sapwood can be protected by preservative treatment. Fungal Degradation – Dry Rot • Removal of any one of these four conditions will prevent fungal attack although, in practice, it is usually moisture that requires the greatest consideration. Fungal Degradation • Timber is best protected from fungal action by: • eliminating contact with moisture, or • where this is not possible, by using species with natural durability appropriate for the application or low durability species or sapwood preservative treated to a level appropriate to the hazard . Durability of Timber • Fungal Attack • Insect Attack • Thermal Attack • Chemical/Liquid Attack Termites • In Australia there are 350 species, but only 30 are regarded as pests. • Termites feed on cellulose in the Timber Structure • This will destroy the Timber structure Termites • 3 Types – Subterranean – Damp wood – Drywood • These Termites are most common • Mainly found north of Tropic of Capricorn • Do not need a connection to ground • H2F Treated timbers are not suitable Durability of Timber • Fungal Attack • Termite Attack • Thermal Attack • Chemical/Liquid Attack Thermal Degradation • Thermal action on timber causes it to degrade through combustion of its chemical components, • Structural capacity, due to the reduction of its cross section by charring and to changes in its mechanical properties of strength and stiffness as a function of its exposure to high temperatures. Thermal Degradation • Charring occurs at approximately 300° C. • Charring acts as an insulator. • Damage still occurs internally due to Chemical Changes caused by heat. Thermal Degradation Thermal Degradation Thermal Degradation Durability of Timber • Fungal Attack • Termite Attack • Thermal Attack • Chemical/Liquid Attack Chemical/Liquid • Water will cause timber to swell • Water will promote Termite/Fungal Activity • Timber is resistant to Acids with a ph. > 2 • Timber is resistant to Alkaline with a ph <10 Marine Environments • 3 Zones – Embedded in Sea Bed – Between Sea Bed & High Water Mark – Above High Water Mark Marine Environment • The greatest hazard occurs between the sea bed & High Water Mark Natural Durability See Handout Natural Durability • Naturally rot-resistant woods • These species are resistant to decay in their natural state, due to high levels of organic chemicals called extractives, mainly polyphenols. Durability of Natural Timbers • Sapwood of any species has little protection Durability of Natural Timbers AS 1684 Timber Properties • AS 1684 Appendix H – List the “Properties” by species of Natural Timbers Notes to the Table Notes to the Table Notes to the Table Notes to the Table Notes to the Table Notes to the Table Notes to the Table Notes to the Table AS1604.1 Preservative Treatment Timber Preservatives • Creosote and modified creosote-based preservatives, e.g. Tanalised K. • Light organic solvent based preservatives (LOSP), e.g. Protim, Tanalised Azure, Timtech Az. • Copper chrome arsenic preservatives (fixed waterborne preservatives) e.g. Tanalised C, Tanalised E, Lifewood, Naturewood, Timtech CX, Timtech Q. • Preservative compounds of boron or fluoride e.g. Polybor, Tanalised B, Timtech BG, Osmose Liquid Boron, Sodium Fluoride Creosote • Timber Based – Soot found in Chimney – Used as Food Preservative • Oil Based – Coal Tar – Oil Tar Creosote • Oil Based in Australia – Oil-tar creosote is derived from the tar that forms during the distillation process used in the manufacture of petrol. – The distillation of the tar from the oil occurs at very high temperatures; around 980°C Creosote • Most suited for heavy duty exterior work, such as – railway sleepers, – bridge decking, – transmission poles, – marine piles and – Fencing – May Achieve up - to H6 Timber Preservatives • Creosote and modified creosote-based preservatives, e.g. Tanalised K. • Light organic solvent based preservatives (LOSP), e.g. Protim, Tanalised Azure, Timtech Az. • Copper chrome arsenic preservatives (fixed waterborne preservatives) e.g. Tanalised C, Tanalised E, Lifewood, Naturewood, Timtech CX, Timtech Q. • Preservative compounds of boron or fluoride e.g. Polybor, Tanalised B, Timtech BG, Osmose Liquid Boron, Sodium Fluoride LOSP • Light Organic Solvent Preservative • H2 Termite Protection • H3 Termite and Rot Protection • Is not corrosive to metals LOSP • This class of timber treatments use white spirit, or light oils such as kerosene, as the solvent carrier to deliver preservative compounds into timber. Synthetic pyrethroids are typically used as an insecticide, such as permethrin, bifenthrin or deltamethrin. In Australia and New Zealand, the most common formulations use Permethrin as an insecticide, and Propaconazole and Tebuconazole as fungicides. While still using a chemical preservative, this formulation contains no heavymetal compounds. LOSP • LOSP treated pine is usually machined to the required lengths and shapes before the treatment is applied. As a result of this less pressure is used in the treatment process and a little less penetration of solution is achieved. This does not affect the longevity of the timber, however it means that LOSP timber must not go in ground and if the timber is cut the cut ends must be resealed with a suitable sealant. LOSP • LOSP timber is frequently coated with a protective oil based primer which is usually pink. This primer is applied to stabilise and protect timber during storage and installation, not as a paint primer. As a result it is recommended that LOSP primed timber be sanded down to remove the primer before painting. LOSP • Un-primed LOSP timber is natural in its appearance as the solution used is clear and hence causes no discolouration of the timber. Like CCA the timber will weather and discolour if not stained or painted. • Dye is usually added to indicate treatment. LOSP • LOSP treated timber is non-corrosive to bolts or nail plates. • LOSP Treated Timber can be painted, stained or oiled. If painting is required, oil based undercoats are recommended. • Unpainted surfaces exposed to the elements need regular applications of a high quality timber finish. • Any residual solvent evaporates after 8-12 hours of opening a pack, leaving the timber odour free. LOSP • With good timber for treatment penetration can be right through the timber. There can be small amounts of untreated heartwood present, therefore where the end is exposed a brush on preservative can be applied. Where the cut end is butted up against a treated section, this may not be necessary, or possible. Heavily planed or rip sawn timber should not be used as this may reduce the protective effect. LOSP Timber Preservatives • Creosote and modified creosote-based preservatives, e.g. Tanalised K. • Light organic solvent based preservatives (LOSP), e.g. Protim, Tanalised Azure, Timtech Az. • Copper chrome arsenic preservatives (fixed waterborne preservatives) e.g. Tanalised C, Tanalised E, Lifewood, Naturewood, Timtech CX, Timtech Q. • Preservative compounds of boron or fluoride e.g. Polybor, Tanalised B, Timtech BG, Osmose Liquid Boron, Sodium Fluoride Copper Chrome Arsenic (CCA) • Chromated copper arsenate (CCA) is a wood preservative used for timber treatment since the mid-1930s. It is a mix of copper, chromium, and arsenic formulated as oxides or salts. It preserves the wood from decay fungi, wood attacking insects, including termites, and marine borers. It also improves the weather-resistance of treated timber and may assist paint adherence in the long term Copper Chrome Arsenic (CCA) • It is a pressure treatment process, where a water based solution of CCA is applied using a vacuum and pressure cycle, and the treated wood is then stacked to dry. During the process, the mixture of oxides reacts to form insoluble compounds, helping with leaching problems. Copper Chrome Arsenic (CCA) During CCA treatment, timber is impregnated with the preservative solution using controlled vacuum/pressure processes. • The ingredients and their roles are: – copper to control fungi – arsenic to control termites – chromium to fix the copper and arsenic in the wood. Copper Chrome Arsenic (CCA) • Recognised by Green tint • Over time small amounts of the CCA chemicals, mainly the arsenic, may leach out of the treated timber. This is particularly the case in acidic environments. Replacement for CCA - ACQ • Alkaline copper quaternary • Water Based Preservative • The treatment is made up – Copper as a fungicide, – and a quaternary ammonium compound, an insecticide which also augments the fungicidal treatment Replacement for CCA - ACQ • Since it contains high levels of copper, ACQtreated timber is five times more corrosive to common steel than normal timber • Suitable Fasteners are required Replacement for CCA – CAC (B) • Copper azole preservative – Copper as a fungicide, – and a azole co-biocide compound, an insecticide which also augments the fungicidal treatment – Similar to ACQ it is likely to attack steel fixings Timber Preservatives • Creosote and modified creosote-based preservatives, e.g. Tanalised K. • Light organic solvent based preservatives (LOSP), e.g. Protim, Tanalised Azure, Timtech Az. • Copper chrome arsenic preservatives (fixed waterborne preservatives) e.g. Tanalised C, Tanalised E, Lifewood, Naturewood, Timtech CX, Timtech Q. • Preservative compounds of boron or fluoride e.g. Polybor, Tanalised B, Timtech BG, Osmose Liquid Boron, Sodium Fluoride Boron • Boric acid, oxides and salts (borates) are effective wood preservatives • Borate treated wood is of low toxicity to humans, and does not contain copper or other heavy metals. • However, unlike most other preservatives, borate compounds do not become fixed in the wood and can readily be leached out. • Should not be used where they will be exposed to rain, water or ground contact. Types of Treatment • Vacuum / Pressure Impregnation: e.g. CCA or Creosote – Is used to achieve deep protection for piles, poles, fencing, building timbers and many types of wood used in domestic and industrial construction. • Double Vacuum / Immersion: e.g. LOSP – Is used for the protection of building timbers not in ground contact, e.g. cladding, decking and fabricated joinery components. • Dip / Spray: e.g. Polybor – These preservatives are designed to protect timber against insect attack and should be used for indoor or sheltered situations above ground. They are popular treatments for softwood house framing • Creosote, modified creosote, and other oil-type preservatives are most suited for heavy duty exterior work, such as railway sleepers, bridge decking, transmission poles, marine piles and fencing. • Fixed water-borne preservatives, which will not leach out even when in contact with running water, are most suitable for domestic buildings, posts, poles, landscaping fencing, cooling towers, decking, cladding, etc. • Light organic solvent preservatives are designed for timbers not in contact with the ground. They should be used for factory assembled joinery, e.g. window frames, and for building at home, e.g. elevated decking, pergolas and fascias. They are also used to provide protection for garden furniture. • You may like the effect of natural weathering, but for the best performance, including long service life, your timber should be treated with a water repellent stain. • Treated timber can be painted or stained just like untreated timber. If paint or stain is not used for the final finish, protection with a water repellent is recommended for best results Durability Requirements Degradation of Other Materials • Timber is mildly acidic • Will encourage the oxidisation of metals Degradation of Other Materials Construction Techniques to assist Durability Construction Techniques to assist Durability Construction Techniques to assist Durability Construction Techniques to assist Durability Construction Techniques to assist Durability Mechanical Degradation Mechanical Degradation • To reduce this hazard – Use Timbers > 800kg per m3 in density Fatigue Timber Finishes • Seasoned • Non Seasoned • Rough Sawn • Dressed What is Seasoned Timber Seasoning of Timbers • Open Air • Kiln Dried • Combination Defects Defects Defects Defects Natural Timbers • Structural • Non Structural Defects • Visual – Structural Defects Listed Sap-Staining Fungi Sap-staining fungi do not attack the cell walls of the wood, only the contents of the wood cells, and so will not decay the timber. The fungus causes a bluish stain in the wood which may make the wood useless for furniture making or veneering for instance. The fungus will thrive in freshly cut timber or unseasoned timber that has not been properly stacked, for instance without stickers. Sap-stain will not occur in correctly seasoned timber. It can be treated with a preservative that will prevent further attack and kill the existing fungus. Blue Stain • A discoloration that penetrates the wood fibre. It can be any colour other than the natural colour of the piece in which it is found. It is classed as light, medium or heavy and is generally blue or brown. Machine Burn • A darkening of the wood due to overheating by the machine knives or rolls when pieces are stopped in a machine. Pitch • An accumulation of resinous material on the surface or in pockets below the surface of wood. Also called gum or sap. Loose Knot • A knot that cannot be relied upon to remain in place in the piece. Caused by a dead branch that was not fully integrated into the tree before it was cut down Tight Knot • A knot fixed by growth or position in the wood structure so that it firmly retains its place in the surrounding wood Wormholes • Small holes in the wood caused by insects and beetles Insect Attack Insect Attack Engineered wood products • A way to reduce the variability of the material • Use low quality material to produce a highgrade product • Use high quality material in high stress zones • No size limitations (almost) • Can be made for special applications Durability • Is dependant on the Base Timber & Adhesive • May be treated to H2 or H3 Adhesive • The Type A phenolic bond, used in structural plywood manufactured to AS/NZS 2269 and structural LVL • manufactured to AS/NZS 4357, will not creep or break-down in applications involving long-term • structural performance and/or extreme longterm exposure to weather, wet or damp conditions. It is a durable, permanent bond. • Transport • Keep timber flat - Timber may twist, bow or cup if transported in a bent condition. It should be bundled and stacked at all stages so that it is flat. This is necessary even for a short trip across town on the back of a truck. • Protect corners of packs - Part of the care of the timber is the use of corner protection under straps used to bind packs. • Protect seasoned timber from moisture – packs of seasoned timber must be wrapped in plastic for delivery and storage on site Delivery • Arrange delivery to fit in with construction sequence –. If possible, it is best to have the timber members that will be used first in the process delivered near the top of any bundles. However, if that is not possible for delivery, then when stacking the timber in the storage area, it should be done so that the first used timber is at the top. • Unload timber – don’t dump! - Firewood is often delivered by raising the truck tray and letting all of the wood roll off onto the ground. The resulting pile of timber will mean that many pieces are bent or twisted and will be much harder for carpenters to install • Use soft slings and protection for timber on corners of packs Storage • Stack timber flat – stacking the timber flat reduces the chance of the timber warping, twisting, bending or cupping prior to installation. (Once restrained by the rest of the structure, deformation in service is less likely.) • Stack timber off the ground - Keep the timber away from ground contact. This prevents attack by termites or grounddwelling fungi, and it also stops the wood from absorbing moisture directly from the ground. Where timber is stacked on gluts or pieces of wood, the gluts should be of higher durability timber to prevent fungi and termites from using the gluts as a route to the timber Storage • Stack the timber in order of use - helps to minimise double handling and to find the pieces with minimum trouble later • Cover all seasoned timber Water on seasoned timber: o Makes it more prone to movement or splitting later on as it dries back out again o Makes the timber more desirable for fungal or insect attack. o Makes it harder to paint, and makes protective coatings less effective. o Stains the timber. Storage • Store appearance products inside building for as long as possible - With many appearance products (such as flooring and lining materials) it is recommended that the material be stored inside the building for as long as possible (some weeks) prior to installation. This allows the material to reach equilibrium moisture content. The timber will change its moisture content slowly to arrive at a moisture content, which is stable with the air inside the building. It is desirable for this to have occurred prior to installation so that the timber doesn’t shrink or swell after it is in service. Shrinkage can crack the product or open unsightly cracks, and swelling may cause buckling Storage Protection during construction • Minimise the exposure of seasoned timber to weather • Cover partially completed work whenever possible • Seal end-grain as soon as possible - End grain of timber presents the ends of the hollow cells to the atmosphere and this can give a conduit for moisture to be transmitted deep into the timber. Often, the end grain is hidden in the structure, as part of the detailing. It is better to seal the end grain of pieces before assembly. In some cases an end cap may prove the better solution. • Apply protective seals or paint finishes as soon as possible – This will preserve the intended appearance of the timber, and offer improved life of the elements.
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